Faulty Earth tests might explain why NASA’s rovers get stuck on Mars

Gravity differences cause NASA rovers to get stuck in Mars' sand.

: Researchers have identified a previously overlooked factor that may explain why NASA's rovers encounter difficulties on Martian soil. While testing rover prototypes on Earth, engineers only accounted for gravity's effect on the rovers but not on the sand. This oversight could cause issues, as Earth's gravity affects sand differently than Mars', making it more rigid. By understanding these dynamics, NASA can better prepare their robots for Mars' challenging terrains.

NASA's Mars rovers, including Spirit and Opportunity, have historically faced issues of getting stuck in soft Martian soil. Recent findings by engineers at the University of Wisconsin–Madison reveal that a key flaw in Earth-based test procedures may be responsible. Simulations of Martian terrain on Earth typically replicate gravity by scaling down the rover’s weight, but they neglect how gravity influences the behavior of the soil itself. This means the test environments on Earth present firmer surfaces than those found on Mars, leading to false assumptions about traction and mobility.

Earth's stronger gravity compresses soil more tightly, giving rovers better grip in tests than they would have on the Red Planet. When engineers conducted extraction trials using Earth sand, rovers appeared more capable of freeing themselves than they truly were on Mars. On the Martian surface, looser and less compact soil causes wheels to sink more deeply, rendering Earth-based escape procedures ineffective. This misalignment became particularly problematic in cases like the Spirit rover, which got permanently trapped in a sand patch in 2009.

To correct this oversight, researchers employed Project Chrono, a physics-based simulation engine, to model how soil and rover wheels interact under different gravitational conditions. Their findings demonstrated that soil mechanics vary drastically between Earth and Mars, even when using identical materials. By virtually recreating rover movement in low gravity, the team revealed how prior test protocols underestimated the difficulty of traversal in Martian regolith.

The analysis also retroactively explains why Spirit became irrecoverably immobilized. Its escape strategies were developed from tests that failed to account for how Martian gravity affects soil deformation. The new research emphasizes that not just the mass but the soil response must be realistically modeled in future Earth-based testbeds. Otherwise, rover designs and rescue plans risk repeating the same failures in upcoming missions.

The takeaway is that accurate simulations of extraterrestrial terrain require more than just scaling weight—they demand rethinking the very physics of wheel–soil interaction under reduced gravity. NASA and other space agencies are expected to adjust their testing methods accordingly, integrating these insights into next-generation rover planning and planetary mobility systems.

Sources: Gizmodo, ScienceDaily, University of Wisconsin–Madison, OrbitalToday, The Debrief

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